Perovskite type ceramic materials have been particularly suitable as ferroelectrics and used in capacitors due to their relatively high dielectric constant (and correspondingly high electrostrictive strains). However, it has been difficult to prepare polycrystalline ceramic perovskite materials such as those having a general formula Pb(A.sub.1/3.sup.2+ B.sub.2/3.sup.5+)O.sub.3 wherein A can be one or more divalent elements Generally, when prepared by sintering from the oxides, a stable pyrochlore phase develops which has a much lower dielectric constant than the corresponding perovskite phase.
S. L. Swartz and T. R. Shrout reported in Materials Research Bulletin, Vol. 17, pp. 1245-1250, 1982 that the above mentioned difficulty, i.e., a formation of the pyrochlore phase, can be eliminated when preparing a lead magnesium niobate by first sintering magnesium oxide together with niobium oxide to form a magnesium niobate having the columbite structure and then sintering this material with lead oxide to form the final desired lead magnesium niobate having a perovskite structure. However, while the technique of forming the precursor was applicable for the preparation of the aforementioned lead magnesium niobate and for lead nickel niobate, it was found that it was not applicable to the formation of a lead zinc niobate, lead aluminum niobate or lead chromium niobate. In the latter three compounds, the pyrochlore phase still resulted even when the zinc, aluminum and chromium. were prereacted with the niobium as taught by Swartz et al.